Genetic change Darwin Evolution and the theory Gene pool variation Natural selection Genetic drift – founders effect, bottleneck effect

So far……… We have looked at Genetic variation Meiosis – crossing over, recombinant Meiosis – segregation Meiosis – independent assortment Mutations Mendelian Genetics – monohybrid cross, dihybrid cross, test cross ( do not use the words back cross) Now we are looking at Genetic change - a permanent change in the gene pool of the population over a period of time (Evolution)

Evolution This is the process by which new species of plants and animals develop from earlier forms The process of evolution normally occurs slowly, usually in response to a change in a species’ environment Evolution proceeds by changes in the frequency of alleles in a population – some alleles do better than others

What is evolution? Evolution refers to the permanent genetic change (change in gene frequencies) in population of individuals. It does not refer to changes occurring to individuals within their own lifetimes. Populations evolve, not individuals. Evolution is not a belief system. It is a scientific concept. Evolution is a theory…but you don’t get any better than that in science Theory: a well-substantiated explanation that incorporates facts, laws, inferences and tested hypotheses.

Recall these keywords Gene pool: all the genes carried by a population at a certain time e.g the all the genes of the fantails in the south Island make up a gene pool Allele frequency: within a population each allele exists at a particular frequency. It is calculated by a simple formula Evolution occurs when frequencies of alleles change over time.

And these…. Species a grouping of organisms that can interbreed and are reproductively isolated from other such groups Population: comprises the total number of one species in a particular area.All members of a population have the potential to interact with each other. This includes breeding.

Compare – genetic change & genetic variation Genetic variation: is the result of two processes Creation of new genes by mutation Reshuffling of existing genes in sexual reproduction Genetic change: changes in the gene pool occurring over successive generations Mutation Natural Selection Mate Selection Migration Genetic drift

Modelling Genetic Change methods You are given a gene pool of individuals showing variation for skin colour. The alleles are given on the sheet of paper in your tray. If nothing affected this gene pool over time, the allele frequency would remain constant. Count your alleles to start with and write them down.

Natural Selection Choose a predator for your group. They will be asked to pick out one at a time as many individuals as they can in 1 minute. After each picking they must spin around once before picking the next one. Now count your alleles, have the ratios changed? Why? Natural selection is the passing on of alleles which are the fittest. Which were the most fit alleles in your tray?

Migration For the alleles that have been eaten, replace with new alleles selected at random from your bag. This time you will choose an allele with your eyes closed and one person will take it to another tray. You may repeat this 10 times. Now count and record your alleles.

Genetic Drift Genetic Drift occurs when a part of a population is cut off or separated from the rest. Using the current population, shake your tray then place a ruler over the tray with your eyes closed. Everything to the left of the ruler dies and need to be removed from the tray. Count and record your remaining alleles in the population. Have any alleles died out?

Mate Selection Green alleles are considered desirable individuals and mate with yellow alleles. Pair these up. Red alleles mate with purple alleles. Pair these up. Any remaining alleles die and need to be removed. What is left?

Keywords Microevolution describes the small-scale changes within gene pools over generations. Macroevolution is the term used to describe large scale changes in form, as viewed in the fossil record, involving whole groups of species and genera. Natural selection: Individuals which have alleles which are more fit than others in the gene pool will survive and go on to reproduce, passing on those fit alleles. Deme: A local unit of population living in a particular area, genetically isolated from other populations.

Theory of Evolution Charles Darwin is credited with the development of the theory of evolution by natural selection, there were many other who contributed. There is a time line of beliefs and scientific argument

History of Evolutionary Thought Erasmus Darwin 1731 - 1802 Charles Darwin's grandfather and probably an important influence in developing his thoughts on evolution. John Baptiste de Lamarck 1744 - 1829 First to publish a reasoned theory of evolution. Proposed idea of use and disuse and inheritance of acquired characteristics. Rev. Thomas Malthus 1766 - 1834 Wrote: ‘An Essay on the Principles of Population’, attempting to justify the squalid conditions of the poor. Hebert Spencer 1820 - 1903 Proposed concept of the ‘survival of the fittest’ Alfred Russel Wallace 1823 - 1913 ‘Theory of Natural Selection’ Charles Darwin 1809 - 1882 ‘Theory of Evolution by Natural Selection’ Charles Lyell 1797 - 1875 Major influence on Darwin. Lyell’s work ‘Principles of Geology’ proposed that the earth is very old. Gregor Mendel 1822 - 1884 Developed the fundamentals of the genetic basis of inheritance. August Weismann 1834 - 1914 Proposed chromosomes as the basis of heredity, demolishing the theory that acquired characteristics could be inherited. Julian Huxley 1887-1975 Ernst Mayr 1904-2005 T. Dobzhansky 1900-1975 Collaborated to formulate the modern theory of evolution, incorporating developments in genetics, paleontology and other branches of biology. R.A. Fisher 1890-1962 J.B.S. Haldane 1898-1964 Sewall Wright 1889-1988 Founding of population genetics and mathematical aspects of evolution and genetics. The New Synthesis Neo-Darwinism: The version of Darwin’s theory refined and developed in the light of modern biological knowledge (especially genetics) in the mid-20th century

Old Theories of Evolution Jean Baptiste Lamarck (early 1800’s) proposed: “The inheritance of acquired characteristics” He proposed that by using or not using its body parts, an individual tends to develop certain characteristics, which it passes on to its offspring.

“The Inheritance of Acquired Characteristics” Example: A giraffe acquired its long neck because its ancestor stretched higher and higher into the trees to reach leaves, and that the animal’s increasingly lengthened neck was passed on to its offspring.

Charles Darwin Influenced by Charles Lyell who published “Principles of Geology”. This publication led Darwin to realize that natural forces gradually change Earth’s surface and that the forces of the past are still operating in modern times.

Charles Darwin Darwin set sail on the H.M.S. Beagle (1831-1836) to survey the south seas (mainly South America and the Galapagos Islands) to collect plants and animals. On the Galapagos Islands, Darwin observed species that lived no where else in the world. These observations led Darwin to write a book. http://science.howstuffworks.com/life/29786-100-greatest-discoveries-natural-selection-video.htm

Darwin discovered these after his voyage…

Charles Darwin Wrote in 1859: “On the Origin of Species by Means of Natural Selection” Two main points: 1. Species were not created in their present form, but evolved from ancestral species. 2. Proposed a mechanism for evolution: NATURAL SELECTION

Natural Selection Overproduction Variation Natural Selection Individuals show variation: some variationsare more favorable than others Overproduction Populations produce too many young: many must die Natural Selection Natural selection favors the best suited at the time Inheritance Variations are inherited. The best suited variants leave more offspring.

Charles Darwin theory of evolution by natural selection was based on: 1. Overproduction Organisms have high reproductive rates – often producing more offspring than needed. This lead to struggle for survival among offspring 2. Variation Among offspring there was variation in all characteristics. Variation in phenotype therefore genotype 3. Favourable variations Organisms with favourable variations better able to survive and pass on those favourable characteristic to offspring 4. Survival of the fittest Over time each successive generation will be better adapted to the environment 5. Evolution Eventually new species evolve from old by the process Darwin called “Natural Selection”

Summary of Darwin’s Theory: Natural selection can provide the means for a species to change over time because natural selection will always favour the most adaptive phenotypes (therefore genotypes). More favourable phenotypes will have greater reproductive success and will become proportionally more abundant in the population. Over time, favourable phenotypes will predominate and the unfavourable phenotypes will become rare.

Video http://www.youtube.com/watch?v=7w57_P9DZJ4 http://www.youtube.com/watch?v=-VSevMUX1QQ